What is the difference between the Standalone, Disaster Recovery and Datacenter modes?

Short answer

The three are selected in the domain's Default Mode field and are the operating modes that determine which data center's addresses the records are answered with; the selected mode is applied to all the records of the domain. Standalone works with a single (local) data center group. Disaster Recovery works active-passive with two groups: answers are given from the Main DC, switch to the DR DC when the switchover condition occurs, and return to the Main DC automatically when the condition clears. Datacenter ranks multiple data centers according to the selected criterion and includes in the answer the healthy addresses of the first N data centers in the ranking (default 1).

How Does It Work?

In every mode, the addresses of the records are kept in data center groups; the mode determines which group is used when an answer is given. In every mode, the addresses are filtered for health by the record's HC condition, and if no candidate remains, the Fail-Safe Records are returned.

Comparison

	Standalone	Disaster Recovery	Datacenter
Data center groups	A single group (local)	Exactly two: Main DC and DR DC; one of them is the local data center	The local data center and the others that are added (DC № 1, DC № 2 …)
Answer	The healthy addresses of the group	Normally the healthy addresses of the Main DC; during a switchover, those of the DR DC	The healthy addresses of the first Total DCs to Select from (default 1) data centers in the ranking
Switchover or selection criterion	None	Disaster Recovery Condition: by default Automatic (when no healthy primary records left), or a health scenario	DC Selection: All DC Records (form order), DC Based, Service Based, Client Based
Required definition	None	The other data center in Remote Devices	The other data centers in Remote Devices
Typical use	A single data center, authoritative DNS, health-aware answers	Active-passive disaster recovery	Active-active, distribution by load or proximity

In TR7

• The mode is selected in the Default Mode field of the domain form (default Standalone); in the domain list, it is seen with the hidden Default Mode column. In the record form, the Record Behavior field shows the mode and cannot be changed.
• The mode-specific settings (the switchover condition, DC Selection, Total DCs to Select from) are made in the record form (Records).
• In the Disaster Recovery and Datacenter groups, the data center is selected from among the local data center and the TR7 devices added to Remote Devices.

Common Misconceptions

• "In Disaster Recovery, when the primary data center recovers, the switch back is made manually." When the switchover condition disappears, the answers return to the Main DC automatically (What are the Disaster Recovery conditions; is the switchover automatic or manual?).
• "In Datacenter mode, all data centers always take part in the answer." By default, only the first data center in the ranking is used; the number is increased with Total DCs to Select from. In Client Based selection, this limit is not applied.
• "Changing the mode later is risk-free." When the domain is saved, the new mode is applied to all records and the data center groups are re-established.

How it is done in the documentation

• Domains · Operating Modes
• GTM (Global Traffic Manager) · Operating Modes
• Records · The Record Resolution Logic

Related questions

• How does the switchover between the primary and backup data centers work in Disaster Recovery mode?
• How is traffic distributed across data centers in Datacenter mode?
• I have a single data center; do I need GTM?
• What is a domain in GTM; how does it relate to a DNS Service?